I'm at the other end of the country so can't help with the prop but I'm running an 18" Vengence stainless on a BF130 on a 6.5 meter Coastline and it's still hitting 6000 RPM, 36 Knots I've just fitted a 20" Laser II (Mercury 15 spline) haven't had it on the water yet but I'm expecting 5600 RPM WOT. Points being.... 15" I would think is way too fine and Mercury Props fit (NOT MERCRUISER) it's a Mercury outboard gearbox Honda used) and they are much easier to come by. There is also a calculator on Honda's web site where you can enter details of your existing set-up/performance and it will recommend the best prop for you. The suggestion for mine was a 21" stainless.
Hope this helps.